When sticking a pressure-sensitive adhesive sheet onto an adherend by hand, entrapment of air between the adherend and the pressure-sensitive adhesive surface may occur, marring the appearance of the pressure-sensitive adhesive sheet. Such air entrapment is particularly prone to occur in the case that the pressure-sensitive adhesive sheet has a large area.
To eliminate problems with appearance of a pressure-sensitive adhesive sheet due to air entrapment, another pressure-sensitive adhesive sheet may be stuck on in place of the original pressure-sensitive adhesive sheet, or the original pressure-sensitive adhesive sheet may be peeled off and then reattached, or a hole may be made with a needle in a blistered portion of the pressure-sensitive adhesive sheet so as to allow the air to escape. However, in the case of sticking on in place of pressure-sensitive adhesive sheet, effort is required, and furthermore the cost is increased; moreover, in the case of reattaching the original pressure-sensitive adhesive sheet, problems often arise such as the pressure-sensitive adhesive sheet tearing, or wrinkles forming on the surface, or the adhesiveness dropping. On the other hand, the method of making a hole with a needle mars the appearance of the pressure-sensitive adhesive sheet.
To prevent air entrapment from occurring, there is a method in which water is put onto the adherend or the pressure-sensitive adhesive surface in advance before the two are stuck together; however, in the case of sticking on a pressure-sensitive adhesive sheet having large dimensions such as a scattering glass preventing film stuck onto a window, a decorative film or a marking film, much time and effort is required. Moreover, there is a method in which air entrapment is prevented from occurring by sticking on the pressure-sensitive adhesive sheet using a device rather than by hand; however, depending on the use of the pressure-sensitive adhesive sheet or the site or shape of the adherend, it may not be possible to use such a device for sticking on the pressure-sensitive adhesive sheet.
Meanwhile, a resin material such as an acrylic resin, an ABS resin, a polystyrene resin or a polycarbonate resin may emit a gas upon heating or even with no heating; in the case of sticking a pressure-sensitive adhesive sheet onto an adherend made of such a resin material, blistering may occur on the pressure-sensitive adhesive sheet due to the gas emitted from the adherend.
Moreover, in the case of sticking a pressure-sensitive adhesive sheet onto an adherend made of a resin through which gas readily permeates, gas that has permeated through may build up between the adherend and the pressure-sensitive adhesive sheet, so that the pressure-sensitive adhesive sheet blisters or peels off. For example, in the case that a marking sheet is stuck onto a polyethylene resin gasoline tank of a motorbike, vapor of gasoline in the gasoline tank may vaporize so as to permeate through the polyethylene resin layer of the gasoline tank, so that the marking sheet blisters or peels off, bringing about an undesirable situation such as the appearance being marred.
To solve such problems, in Japanese Utility Model Registration No. 2503717 and Japanese Utility Model Registration No. 2587198, there is proposed a pressure-sensitive adhesive sheet in which a large number of independent small protruding portions are disposed scattered over a pressure-sensitive adhesive surface of a pressure-sensitive adhesive layer. In this pressure-sensitive adhesive sheet, a state is maintained in which the tips of the small protruding portions of the pressure-sensitive adhesive layer are in close contact with the adherend and hence a basic flat surface of the pressure-sensitive adhesive layer is separated away from the adherend, whereby gaps that communicate with the outside arise between the basic flat surface of the pressure-sensitive adhesive layer and the adherend, and hence air or gas can escape to the outside from these gaps, thus preventing air entrapment or blistering of the pressure-sensitive adhesive sheet.